"notch, groove, slit," late 15c., nyke, of unknown origin, possibly influenced by Middle French niche (see niche), or from it. Nick of time is first attested 1640s (nick of opportunity is 1610s), possibly from an old custom of recording time as it passed by making notches on a tally stick, though nick in the general sense of "critical moment" is older (1570s, Hanmer, who adds "as commonly we say") than the phrase.